Method for auto-configuration of a wavelength selective switch in an optical network

ABSTRACT

The invention relates to a method for auto-configuring a wavelength selective switch (WSS) device having an output port and a plurality of input ports and coupled to a WSS controller. When connected to a WDM optical network, the WSS controller is programmed to utilize one or more optical channel monitors (OCM) coupled to the input and/or output ports to detect which of the wavelengths are present at the input ports. Wavelengths that are not detected on any input port are blocked by the WSS. Any wavelength detected as present at one and only one input port is switched by the WSS to the output port. If a wavelength is detected at two or more input ports, it is either blocked by the WSS at each of the input ports until user intervention, or is blocked at all but one of the input ports as defined by assigned port priorities.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims priority from U.S. Provisional PatentApplication No. 61/155,979 filed Feb. 27, 2009, entitled “Method ofSelf-Configuring a Controlled WSS or a ROADM device”, which isincorporated herein by reference for all purposes.

TECHNICAL FIELD

The present invention relates generally to wavelength multiplexedoptical communication systems and methods, and more particularly relatesto methods of operating wavelength selective switches in such networks.

BACKGROUND OF THE INVENTION

Modern optical communication networks conveniently employ multi-channelwavelength-multiplexed optical signals. Such signals are comprised of aplurality of spectral channels, each having a distinct center wavelengthand an associated bandwidth. The center wavelengths of adjacent channelsare spaced at a predetermined wavelength or frequency interval, and theplurality of spectral channels may be wavelength division multiplexed(WDM) to form a composite multi-channel, or WDM, signal of the opticalnetwork. Each spectral channel, also referred to herein as thewavelength channel or simply the wavelength, is capable of carryingseparate and independent information. At optical switching nodes in theoptical network, one or more spectral channels may be dropped from oradded to the WDM optical signal, as by using, for example, areconfigurable optical add-drop multiplexer (ROADM).

A ROADM at the optical switching node may be constructed using one ormore wavelength selective switches (WSS) configured as ADD and/or DROPmodules. Wavelength selective switching in telecommunications networksis a relatively new technology that enables agility at the physical,i.e. optical, layer of the network. It allows wavelengths carrying dataof any protocol or at any rate to be quickly and dynamically re-directedthrough networks to accommodate changes in demand for bandwidth, orchanges in network topology, such as due to addition of new nodes to thenetwork, addition of new wavelengths or services to the network,failures of links or nodes within the network, etc. Examples of WSS andROADM devices are disclosed in U.S. Pat. Nos. 6,487,334; 6,498,872;6,549,699, 6,625,346, 6,661,948, 6,687,431, 6,760,5116,707,959;7,039,267; 7,027,684; 7,302,134; 7,236,660; 7,212,704, which areincorporated herein by reference.

WSS technology that is available today supports switching of 80 or morechannels through a single device, with the port count of a typical WSSbeing between typcially 3 and 10 or even greater. One type of WSSdevices conveniently used today has one ‘common’ port, while all othersare ‘add/drop’ ports, where each supported wavelength can be routedbetween the common port and any one, and typically only one, of theadd/drop ports, or ‘blocked’ entirely (i.e., highly attenuated).However, this or similar technology could be extended to support muchgreater numbers of wavelengths and ports, or to support the ability toroute wavelengths between any two ports. Note that WSSs are typicallybi-directional in nature. That is, once the path for a given wavelengththrough the WSS has been configured from one port to another, modulatedor unmodulated light of that wavelength can propagate in eitherdirection between the two ports.

Advantageously, WSS technology enables reconfiguration of wavelengthpaths through networks using software control, without the need fortechnicians to change physical connections between devices in thenetwork, such as to change optical fibre connections between fixedoptical multiplexer/demultiplexer devices at network nodes wherewavelengths are being added to or dropped from the optical network.However, despite the existence of the ability to perform wavelengthreconfiguration remotely, control of telecommunications networks todaystill often relies on human intervention to determine the optimalwavelength configuration, and then to implement or initiate the desiredchange.

Human intervention may be particularly intense during deployment andcommissioning of new WSS devices in a network, when operators musttypically configure each supported wavelength. In some cases,network-level control software is used to reduce this burden by allowingthe operator to configure a wavelength path through the entire network,and automating the configuration of individual WSS devices and ROADMnodes within the network.

However, this approach may also have certain disadvantages. Inparticular, smaller and simpler networks involving WSS/ROADM technologyoften don't warrant the increased cost and complexity of this networklevel control. Furthermore, network-level wavelength configurationapproach necessitates having a computer or server that requirescontinuous software access to all nodes in the network in order tore-configure it. Furthermore, network operators may want to be able tointroduce WSS or ROADM technology into existing networks without havingto entirely change the method in which the network is managed, or toreconfigure the network management software at the control node.

Accordingly, a solution is desired that would enable to automate, orreduce the burden of, configuring WSS devices at the individual WSSdevice or network element (network node) level without the intervention,or in the absence of, network-level software of this kind.

An object of the present invention is to provide a means by whichwavelength configuration in a network may be simplified and/or automatedand, WSS devices in a WDM optical network may be automaticallyconfigured at the WSS device and/or network node level without thedrawbacks of network-level wavelength control.

SUMMARY OF THE INVENTION

In accordance with the invention, there is provided a method foroperating a wavelength selective switch (WSS) device in a wavelengthdivision multiplexed (WDM) optical network, the WSS device having anoutput optical port and a plurality of input optical ports, and beingcoupled to a WSS controller for selectively provisioning opticalconnections between the input optical ports and the output optical portat one or more of a plurality of supported wavelengths. The methodcomprises: a) determining which of the supported wavelengths arereceived at each of the input ports using at least one optical channelmonitor (OCM) coupled to the WSS device; and, b) using the WSScontroller to selectively provision optical connections from respectiveinput optical ports to the output optical port at those of the supportedwavelengths that are received at a single input optical port of the WSSdevice, and to block connections between the input optical ports and theoutput optical port at those of the supported wavelengths that are notreceived at any of the input optical ports.

In accordance with one aspect of this invention, the method comprisesthe steps of: c) receiving, by the WSS controller, information from theat least one OCM which of the supported wavelengths are present at atleast one of the input optical ports; d) based on the informationreceived from the at least one OCM, determining by the WSS controllerwhich of the received wavelengths are present at one and only one of theinput optical ports; and, e) at each of the wavelengths identified instep (d), provisioning by the WSS controller an optical connection inthe WSS device between a corresponding input optical port and the outputoptical port.

Another aspect of the present invention provides a WSS device comprisinga WSS element having an input port and a plurality of output ports forselectively switching any of a plurality of supported wavelength fromany of the input ports to the output port or for blocking thereof, theWSS device further comprising a WSS controller coupled to the WSSelement for controlling the switching, and further comprising one ormore optical channel monitors coupled to the input and/or output portsof the WSS element and to the WSS controller, wherein the WSS controlleris programmed to auto-configure the WSS element that is connected in anoptical WDM network, by performing the steps of: co-operating with theone or more OCM to detect the presence of the supported wavelengths ateach of the input ports; and, controlling the WSS element in such a waythat i) any the supported wavelengths that is not detected by the OCM atany of the input ports is blocked by the WSS element from reaching theoutput port; ii) any wavelength whose presence is detected by the OCM atone and only one of the input ports is switched to the output port; and,iii) any supported wavelength whose presence is detected at more thanone of the input ports is either blocked at each of the input portsuntil user intervention, or is blocked at all but one of the input portsand is directed to the output port from one of the input ports receivingsaid wavelengths which has a comparatively higher priority assignedthereto.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail with reference to theaccompanying drawings which represent preferred embodiments thereof,wherein:

FIG. 1 is a block diagram of an exemplary controlled WSS deviceaccording to the present invention;

FIG. 2 is a block diagram of a WSS device having an optical channelmonitor at each input port;

FIG. 3 is a block diagram of a WSS device having an optical channelmonitor at each input port;

FIG. 4 is a block diagram of a WSS device having a single opticalchannel monitor connected to the input ports thereof with a portselector switch;

FIG. 5 is a general flowchart of the method for auto-configuration of aWSS device according to the present invention;

FIG. 6 is a flowchart of one embodiment of the method forauto-configuration of a WSS device according to the present invention;

FIG. 7 is a flowchart of another embodiment of the method forauto-configuration of a WSS device according to the present invention;

FIG. 8 is a flowchart of a process for detecting the presence ofsupported wavelengths at each of the input ports of the WSS device usingan OCM coupled to the output port thereof;

FIG. 9 is a flowchart of one implementation of the method forauto-configuration of a WSS device according to an embodiment of thepresent invention;

FIG. 10 is a block diagram of an exemplary linear section of a WDMnetwork wherein the method of the present invention may be applied.

DETAILED DESCRIPTION

One aspect of the current invention provides a means by which acontrolled WSS device can automatically configure itself based on thedetection of wavelengths, i.e. wavelength-multiplexed optical channels,present at one or more inputs into the device. In the followingdescription, the operation of a WSS device will be considered in thecontext of a WDM optical network which supports a plurality ofwavelength-multiplexed optical channels, which central wavelengthsλ_(i), i=1, . . . , N, are typically spaced uniformly in frequency andlie on a pre-defined grid, for example corresponding to 50 GHz, 100 GHzor 200 GHz frequency spacing. However, it will be appreciated that theuniform in frequency spacing of the supported wavelengths channels isnot a requirement for the present invention. In the context of thisspecification, we will be referring to the supported wavelength channelssimply as the wavelengths, according to the channel central wavelengthsλ_(i), so that the presence of a wavelength at a port of an opticaldevice is understood as the presence of an optical signal of a suitablestrength which spectrum is centered at said wavelength. The number N ofsupported wavelengths in the network may be network-specific, withtypical examples being 8, 10, 40 and 80.

With reference to FIG. 1, an exemplary configuration of a controlledWSS, denoted as a WSS device 100, is illustrated. In the context of thisspecification, the term “wavelength selective switch”, or WSS, is usedto refer to a wavelength-switching element that is capable ofselectively switching wavelengths from any number of input ports to oneoutput port, and/or vice-versa. Many types of WSSs are known in the art,some of which are described in U.S. Pat. Nos. 6,487,334; 6,498,872;6,707,959; 7,039,267; 7,027,684; 7,302,134; 7,236,660; 7,212,704, whichare incorporated herein by reference. Typically, a WSS includes adispersive element for separating light into constituent wavelengths orfor combining multiple spatially dispersed wavelengths into a singleoutput light beam, and an electrically controlled array of lightmanipulating elements such as a MEMS array or an LC cell array forattenuating or blocking dispersed light on a wavelength by wavelengthbasis. The term “Controlled WSS device” is used to mean a WSS that iscontrolled, for example, configured and monitored, by software orfirmware running on a suitable controller or processor (CPU) that isconnected to it. Configuring the WSS device includes configuringwavelength paths through the WSS device from the input ports to theoutput port, and may optionally include configuring of the opticaloutput power of each wavelength. In the following, the term “WSS device”may be also used to refer to a controlled WSS device.

In the embodiment of FIG. 1, the controlled WSS device 100 includes aWSS element 110, which has an output optical port 112 and n>1 inputoptical ports 111 ₁ to 111 _(n), hereinafter generally referred to asthe input ports 111. The WSS 110 has a control port and is operativelyconnected to a WSS controller 115, to receive control signals therefromfor selectively provisioning or blocking optical paths or connectionsbetween each of the input ports and the output port at any, or at leastsome, of the supported wavelengths individually. The h WSS controller115 may be embodied using a suitably programmed microprocessor or thelike, and is programmed or otherwise configured to generate signals forselectively provisioning optical connections between each of the inputports 111 and the output port 112 at any, or at least some, of thesupported wavelengths λ_(i), or blocking such connections at any of thewavelengths. The WSS controller 115 for controlling the operation of theWSS 110 may be physically located in the same module as the WSS 110, orit may be co-located on a printed circuit board assembly (PCBA) with theWSS element 110, as illustrated in FIG. 1; or it may be located on aseparate PCBA that can communicate with the WSS element 110; orotherwise depending on application. In a preferred embodiment, the WSScontroller 115 for controlling the operation of the WSS 110 isco-located with the WSS 110 at the same node.

The WSS device 100 also includes at least one optical channel monitor(OCM) 125, which is capable of monitoring the presence of supportedwavelengths λ_(i) at the input and/or output ports of the WSS 110, andin some embodiments is also capable of measuring the optical channelpower at said wavelengths as known in the arts.

In the embodiment shown in FIG. 1, the OCM 125 is optically coupled atthe output port 112 for monitoring the wavelength content of the WSSoutput, and is also operatively coupled to the WSS controller 115, whichis programmed to collect results of the optical channel monitoring fromthe OPM 125. There are many technologies available for detecting channelpresence on an optical fiber and suitable for utilizing the OCM 125,including but not limited to, a WDM de-multiplexer coupled to an arrayof photo detectors, an OSA-like device, etc; suitable OCMs utilizingthese and other suitable technologies are well known and commerciallyavailable. Alternatively or concurrently, other OCMs 125 ₁-125 _(n) maybe coupled to each of the input ports 111 of the WSS 110 as illustratedin FIG. 2 to monitor the presence and, optionally, power of opticalchannels at the input ports 111 of the WSS 110.

With reference to FIG. 3, in another embodiment the optical channelmonitoring at the input ports 111 of the WSS 110 may be carried outusing a single OPM 125 connected to the plurality of input ports 111through a port selection switch 140, thereby enabling sequentialmonitoring of the wavelength content at each of the input ports 111. Inthis embodiment, the controller 115 (not shown in FIG. 3) is alsooperatively coupled to the port selector switch 140 for controllingthereof.

With reference to FIG. 4, there is schematically illustrated anexemplary two degree bidirectional node of a WDM optical networkutilizing two controlled WSS devices. The node includes tworeconfigurable optical add-drop modules (ROADM) 201 and 301, whichenable selectively adding and dropping wavelength onto and from thenetwork. Each of the ROADMs 201 and 301 includes an input passiveoptical splitter 230, 330, each of which having a single input port 231,331 for receiving a WDM optical signal propagating in the network in arespective direction, and a plurality of output optical ports 232, 332;one of the output ports serves as an express output port, while one ormore of the other output ports serving as drop ports, as indicated inFIG. 4. Each of the ROADMs 201 and 301 further includes an outputcontrolled WSS device substantially similar to the controlled WSS device100, and comprised of a WSS element 210, 310 coupled to a WSS controller215, 315. Although not shown in FIG. 4, each of the controlled WSSdevices of the ROADMs 201, 301 include one or more OCMs as illustratedin FIG. 1, 2, or 3 for monitoring the wavelengths at the inputs and/orthe output of the respective WSS.

Each of the WSS 210, 310 has a single output port 212, 312 for launchinga WDM optical signal from the node into the network in a respectivedirection of propagation. Each of the WSS 210, 310 further has aplurality of input optical ports 211, 311, with one of the input ports211, 311 serving as an express input port, while one or more of theother input ports 211, 311 serving as add ports for adding wavelengthsto the network, as indicated in FIG. 4. In each propagation direction,the express output port of a respective one of the splitters 230, 330 isconnected to the express input port of a respective one of the WSS 310,210. Considering by way of example the propagation of the WDM signalthrough the node in one of the propagation directions, for example, fromleft to right in FIG. 4, the WDM signal from the network is firstreceived in the input optical port 231 of the splitter 230, which splitsbetween the output ports 232, with each received wavelength present ateach output port. Optical signals from the drop ports of the splitter230 are then dropped from the network; for example, they may bede-multiplexed and then passed to a different local network and/or toend users, or converted to electrical signals as known in the art.

A portion of the input WDM signal is passed from the express output portof the splitter 230 onto the express input port of the WSS 310.Simultaneously, the WSS 310 may also be receiving other “add” opticalsignals at other input ports thereof designated as the “add” ports, foradding those “add” optical signals onto the network. The WSS operates toselectively and reconfigurably combine “express” wavelengths receivedfrom the splitter 230 with the “add” wavelengths received at the “add”input ports of the WSS 310. In doing so, the WSS 310 may also have toblock from the “express” optical signal received at the express inputport those of the wavelengths that were dropped at the splitter 230, inparticular if the “add” optical signals at the “add” input ports 311 ofthe WSS 310 are carried by same wavelengths.

Accordingly, the WSS 310 has to be configured so as to provide opticalconnections from the input ports thereof to the output port atport-specific wavelengths, and to block some of the wavelength dependingon network requirements. Generally, configuring a ROADM such as thatillustrated in FIG. 4 requires configuring its constituent WSS devices,which includes configuring of wavelength paths through the device, andmay also include the configuration of the optical output power of eachwavelength at the output of the WSS device. Heretofore, configuringROADMs and WSSs in optical networks has been performed, or suggested tobe performed remotely from a central control node using sophisticatednetwork control software operating over a control layer of the network.

The present invention provides a method for automated self-configurationof the WSS devices in an optical networks, and in particular at ROADMnodes of optical network. The method provides a means by which acontrolled WSS device can automatically configure itself based on thedetection of wavelengths (channels) present at one or more inputs intothe device.

According to one aspect of the present invention, the WSS controller 115(215, 315) is programmed to control and/or cooperate with the at leastone OCM 125 to detect the presence of the supported wavelengths at eachof the input ports 111 (211, 311 respectively), and to control the WSS110 (210, 310) in such a way that i) wavelengths (channels) that are notdetected by the respective OCM on any input port 111 (211, 311) areblocked by the WSS 110 (210, 310), ii) any wavelength whose presence isdetected by the OCM at one and only one of the input ports 111 (211,311) is switched to the common output port 112 (212, 312), and iii) anywavelength whose presence is detected at more than one of the inputports 111 (211, 311) is either blocked at each of the input ports untiluser intervention resolves the conflict, or is blocked at all but one ofthe input ports 111 (211, 311), and is connected to the output port fromone of the input ports receiving said wavelengths which has acomparatively higher priority assigned thereto.

Except for possibly initiating it, the method requires no userinteraction or external control, such as from software running on aprocessor that is external to the controlled WSS element, to completethe WSS configuration, and therefore simplifies and reduces the amountof user interaction required in order to configure the device. Themethod may be initiated by software command to the controller that isdirectly controlling the WSS, direct physical input from an operator,such as a pushbutton or switch, or any other means. The method requiresthe ability for the WSS controller in the controlled WSS device tomonitor the presence of optical channels on each input portindividually. Optionally, embodiments of the method may also provide amechanism by which the output power of each channel is automaticallyadjusted. Channel powers may be adjusted in one of the following ways:to achieve a pre-determined power profile with respect to one another,including (but not limited to) a flat profile where all channels areoutput from the device with the same optical power level; and/or toachieve a pre-determined absolute power for each channel.

The adjustment of the channel power requires that the controlled WSSdevice supports, within the WSS element itself or otherwise, variableattenuation of optical power levels on a per-channel, or per-wavelengthbasis; one skilled in the art will appreciate that known in the art WSSdevices often include the per-channel variable attenuation capability bydesign, which can be advantageously used by the present invention.

The method for automatic self-configuration of a WSS device, which mayalso be used as an automated start-up procedure thereof, will now bedescribed with reference to FIGS. 5-7 illustrating steps of the methodin various embodiments thereof, and also with reference to thecontrolled WSS device 100 of FIG. 1 by way of example; it will beappreciated that the method steps described hereinbelow are equallyapplicable to the WSS devices 210, 310 in the ROADM Degree 1, 2 modulesillustrated in FIG. 4.

Referring first to FIG. 5, there is shown a flowchart illustrating basicsteps of the method in one embodiment (1) thereof. As illustrated, themethod may include the following general steps:

At step 5, one or more OCMs, such as the OCM 125 in the embodiment ofFIG. 1 or FIG. 3, or the plurality of OCMs in the embodiment of FIG. 2,are used to detect which of the supported wavelengths λ_(i) are receivedat each of the input optical ports of the WSS 110. The WSS controller115 collects resulting information, for example in the form of listingsof wavelengths determined to be present at each of the n input ports 111of the WSS 110.

At step 10, the WSS controller 115 operates the WSS device 110 so as toselectively provision optical connections from respective input opticalports 111 to the output optical port 112 for those of the supportedwavelengths λ_(i) that are received at one and only one of the inputoptical ports 11 of the WSS device.

At step 12, connections between the input optical ports 111 and theoutput optical port 112 at those of the supported wavelengths that arenot received at any of the input optical ports, are blocked within theWSS 110. In one preferred embodiment, the WSS controller 115 may operatethe WSS 110 so as to block, for each of the input ports 111, allsupported wavelengths that are not received at that port.

The WSS controller 115 maybe programmed in such a way that theaforedescribed steps 110 are performed as an automated start-upprocedure when the controlled WSS device 100 is first connected into anetwork. In some embodiments, the WSS 110 may be initially provided in adefault state wherein the connections between each of the input ports111 and the output port 112 are blocked for all supported wavelength; inthat case, step 112 is not required, and the WSS controller 115 willonly need to signal to the WSS 110, which of the received wavelengthsare to be “unblocked” at each of the input ports 11 to couple to theoutput port 112.

In some cases, a same supported wavelength may be present at two or moreof the input ports 111, indicating a wavelength conflict which needs tobe resolved. Such a wavelength conflict may be resolved by eithertemporally blocking the wavelength's passage to the output port fromeach of the input ports where it is detected and awaiting a user inputresolving the conflict, or, in embodiments wherein the input ports areassigned priorities which are made known to the WSS controller, byselecting one of said input ports for opening a path therefrom to theoutput port for the wavelength in conflict according to the portspriorities, while blocking the passage of the conflicting wavelength inthe WSS 110 from all other input ports 111. The auto-configurationalgorithm that is carried out by the WSS controller may also bepre-configured to favor one or more of the input ports, for example, aport that is being used as the ‘express’ port in the ROADM nodeconfiguration such as illustrated in FIG. 4. If a conflicting wavelengthhas been detected on one such favored port and one or more non-favoured,e.g. “add”, ports, the method will automatically configure the WSS toallow the wavelength to pass from the favored input port to the commonoutput port, and block the wavelength on all other ports. In oneembodiment, if a conflicting wavelength has been detected on more thanone favored port, the method will block the conflicting wavelength onall input ports, complete the algorithm, and notify the operator of theconflict.

Referring more specifically to FIG. 6, there is illustrates anembodiment 2 of the method wherein the controlled WSS device 100 isprogrammed to perform the following steps:

At step 5, the WSS controller 115 obtains information from the one ormore OCMs 125 about the supported wavelengths that are present at eachof the input ports 111 of the WSS 110. The WSS controller 115 isprogrammed to identify wavelength conflicts by verifying if any of thedetected wavelengths is present at two or more of the input ports 111.For each of the wavelengths which presence has been detected by the CPM125 at one and only one of the input ports 111, the WSS controller 115provisions at step 10 an optical connection from an input port 111,wherein said wavelength has been detected, to the output port 112 (theI/O connection).

If in step 15 the WSS controller 115 determines that a wavelengthconflict is present, the WSS controller signals to the WSS 110 to blockthe conflicting wavelength or wavelengths in the WSS 110 from reachingthe output port 112 from any of the input ports 111, including the inputports where their presence have been detected by the OCM 125.Optionally, an alarm may be generated at this point that signals that anexternal intervention is required to resolve a conflict.

At step 20, upon receiving a user input indicating which of the inputports 111 receiving the conflicting wavelength should be coupled at saidwavelength to the output port 112, the WSS controller 115 operates theWSS 110 so as to optically couple the selected by the user input port tothe output port 125 for the conflicted wavelength. In an optional step25, the WSS controller 115 may operate the WSS 110 to block opticalconnections between each of the input ports 111 and the output port 112at those of the supported wavelengths that were not detected as presentat a corresponding input port.

With reference to FIG. 7, an embodiment of the method is illustratedwherein the input ports 111 are assigned priorities, which are known tothe WSS controller 115; for example, the WSS controller 115 may include,or be operatively coupled to, a memory element wherein the port priorityinformation is saved, such as in a look-up table. For example, those ofthe input ports 111 that are designated as “add” ports, see FIG. 4, mayhave higher priority associated therewith than the “express” input port,or vice versa depending on a particular system design. Furthermore, someor all of the “add” ports may also have differing priorities assignedthereto. Accordingly, in the embodiment of the method illustrated inFIG. 7, step 10 of provisioning I/O connections for each of thewavelengths that is detected at one and only one of the input ports 111,is accompanied by step 15 a, wherein the WSS controller 115 identifies awavelength λ_(k) that is present at two or more of the input ports 111,thereby detecting a wavelength conflict, and, based on the port priorityinformation that is saved in the memory of the WSS controller,identifies among the input ports 111 receiving said wavelength λ_(k) theport that has the highest priority among all the ports 111 at which thewavelength λ_(k) has been detected, and then provisions an I/Oconnection at the wavelength λ_(k) between the output port 112 and theidentified input port 111 with the comparatively highest priority, whileblocking the passage of said wavelength from all other input ports.

In an optional step 27, the WSS controller 115 may operate the WSS 110so as to set the output optical power of each of the supportedwavelengths that reach the output port 112 according to pre-determinedpower settings. In doing so, the WSS controller 115 may utilize theper-wavelengths optical power readings obtained from the OCM 125, andper-wavelength optical attenuation capabilities that many types of knownWSS devices posses. This step may also be optionally perfumed in theembodiments of FIGS. 5 and 6.

The method of the present invention requires that the WSS device 100 hasthe capability of detecting which of the supported wavelengths arepresent at each of the input ports 111, or receives this informationelsewhere. This can be easily accomplished in the embodiments whereinthe WSS device 100 has one or more OCMs connected in a way that enablesmonitoring of the input ports 111 individually, for example as shown inFIGS. 2 and 3. However, it may be advantageous to have a single OCMconnected at the output of the WSS 110, as illustrated in FIG. 1; apartfrom requiring less hardware, this also enables the direct monitoring ofthe optical power in each of the wavelength channels at the output ofthe WSS 110, thereby facilitating the setting of the output power levelsfor each of the wavelengths. In such embodiments, the step of detectingthe wavelengths that are present at each of the input ports 111 of theWSS 110, i.e. step 5 in FIGS. 5-7, may be carried out as illustrated inFIG. 8. In this embodiment, the WSS controller 115 is programmed toperform, at the start of the WSS auto-configuration procedure, thefollowing steps:

At step 50, the WSS controller 115 directs the WSS 110, i.e. by sendinga suitable control signal to the control port thereof, to blockconnections between the output port 112 and all but one of the inputports 111 at all of the supported wavelengths, so as to open an opticalpath to the output port from a single selected input port. At step 55,the OCM 125 is operated so as to detect which of the supportedwavelengths are present at the output port 112, thereby establishing thewavelength channels that are present at the selected input port. Steps50 and 55 are then repeated each time selecting a different input portto connect to the output port, until all input ports are tested, whilesaving thereby obtained port/wavelength information in the controllermemory.

It will be appreciated that the basic steps of the method of the presentinvention in various embodiments thereof as described hereinabove withreference to FIGS. 5-8 may be implemented using the WSS controller 115or the like in a variety of ways, one of which is illustrated in FIG. 9,showing a flowchart of the logic that the WSS controller 115 may beprogrammed to carry out during the self-configuring of the WSS 100.

The aforedescribed method for auto-configuration of the WSS device in anoptical network provides means by which a ROADM node comprised of one ormore WSS devices, such as that illustrated in FIG. 4, can automaticallyconfigure itself based on the detection of wavelengths (channels)present at one or more inputs into the node. Except may be forinitiating it, the method requires no user interaction to complete theWSS configuration and therefore simplifies, and reduces the amount of,user interaction required in order to configure the ROADM. The methodmay be initiated by software command to the node, direct physical inputfrom an operator, such as a pushbutton or switch, or any other suitablemeans as would be known in the art.

Configuration of the ROADM node may include the configuration of some orall wavelength paths through the node, as well as the configuration ofsome or all optical output power levels of wavelengths at the output ofthe node.

Although many architectures of a ROADM node are possible, FIG. 4illustrates a common architecture wherein a WSS (210, 310) is used toadd wavelengths to a ROADM degree, and a power splitter (230, 330) isused to drop wavelengths at the node. Other possibilities include use ofa WSS for both adding and dropping, or a WSS for dropping and an opticalpower coupler or a fixed Wavelength Division Multiplexer for adding.Distribution of control functions in the node can vary betweencentralization of these functions for all ‘degrees’ on a single controlelement, to increasing distribution of these functions across otherCPUs, or controllers, within the node, which may physically exist ondiverse printed circuit board assemblies within the domain of the samelogical node. By way of example, FIG. 4 illustrates a node controlarchitecture with a common node controller 205 with a processor 255,where control functions that span diverse physical elements within thenode are centralized, and separate WSS controllers 215, 315 for eachdegree of the ROADM node. In other embodiments, the node controller 205may assume functions performed by the WSS controllers 215, 315.

One aspect of the invention provides an automated start-up procedure fora multi-degree ROADM node in an optical network utilizing WSS devicesfor adding wavelengths onto the network, such as the 2-degree ROADM nodeillustrated in FIG. 4. Although not shown in FIG. 4, the method utilizesOCMs coupled to the each of the WSS devices as described hereinabove fordetecting the presence of supported wavelength at each of the inputports of the WSSs, and optionally for monitoring the optical power ineach of the wavelengths appearing at the output port of the respectiveWSS.

Generally, the method may include performing the aforedescribed WSSauto-configuration procedures, see FIGS. 5-8, for each of the WSSdevices used to add channels to the network, such as the WSS devices 210and 310 of the node of FIG. 4. In particular, the method in one aspectthereof may include all or some of the following features:

a) at each degree of the ROADM node, the input ports 211, 311 to the WSSdevice 210, 310 may be designated as Add or Express inputs, with theoutput port 212, 312 designated as Common;

b) wavelengths (channels) that are not detected on the Add or Expressinputs to a given node degree are blocked;

c) any wavelength whose presence is detected at one and only one Add orExpress input is switched to the Common output port.

d) any wavelength whose presence is detected on both an Express inputand an Add input of the same degree are assumed to be added at the node.Therefore the wavelength is blocked on the express input, and routedfrom the Add input to the Common output, such as from one of the “Add”input ports 311 to the output port 312 of the WSS 310.

e) any wavelength whose presence is detected at more than one “Add”input, or more than one Express input for nodes with the number ofdegrees greater than 2, is blocked until user intervention resolves theconflict, or resolved automatically if one of the “Add” input portsreceiving the wavelengths has a comparatively higher priority assignedthereto.

Note that blocking a supported wavelength when it is not detected on anAdd or Express port of the same degree of the ROADM node is advantageousas it enables to avoid potential wavelength conflicts downstream atanother node in the network. Furthermore, blocking of the wavelengththat is not detected at the WSS inputs allows the corresponding channelto be added in a graceful, controlled manner in the future. For example,it would not be unusual for a technician to plug in a transponder of aparticular wavelength and connect it up to the network. If thatwavelength were unblocked through all the switching elements in thenetwork, there are a number of potential problems that could arise, suchas conflicts with other channels in the network or a sudden powertransient.

A wavelength is generally considered to be “blocked” at a selected inputport of the WSS, when the attenuation it experiences on the way fromthis input port to the output port exceeds a pre-determined value,typically 20 dB or greater, or as specified by the system design. Thisfunction is typically implemented within the WSS element itself, as WSSdevices typically support wavelength power control as well as theswitching between optical ports. However, this does not necessarily haveto be the case: A WSS could be used to perform the switching, and aseparate suitable device could perform the wavelength power control,although this may be less efficient and more costly.

The auto-configuration procedure of the present invention in one of theaforedescribed or similar embodiments thereof may be advantageouslyutilized in various network scenarios, such as at a first start-up ofthe network or a section thereof, or when replacing one or morecomponents of a ROADM node, such as the WSS device itself, orperiodically during the operation, etc.

Turning now to FIG. 9, there is schematically illustrated a portion of aWDM network in the form of a linear chain of 2-degree ROADM nodes orsites connected by fiber-optic links between two terminal sides whereinexpress WDM optical signals are terminated, i.e. generated and convertedinto electrical signals. The chain is bi-directional, including twosubstantially identical one-directional chains utilizing a fiber pairformed of two optical fibers for transmitting signals in the oppositedirections. By way of example, a self-configuration start-up procedurefor such a network can be performed using features of the presentinvention as described hereinbelow. For clarity of the description only,it is assumed hereinbelow that the ROADM chain of FIG. 9 is being turnedup from left to right in one direction of the fibre pair, which isreferred to as “east-bound”, then right to left for the other, i.e. the“west-bound”, direction. The term “operator” used hereinbelow may referto a person, group off persons, or to a suitable software running on oneor more processors, which may be either co-located at a same controlsite, or distributed between sites and communicating over a controllayer of the network, or otherwise.

A) First, at terminal site #1, operator ensures that all terminalequipment, such as transponders, are connected so that all desired DWDMwavelengths are present on the output fibre that is facing ROADM site#1, as indicated in the figure by a right-directed arrow. Operatorproceeds to ROADM site #1

B) At ROADM site #1, operator ensures that all desired add/drop WDMwavelengths are connected and present, at least at ROADM degree 2, thenactivates the self configuration algorithm of the WSS on ROADM degree 2,as described hereinabove. If no internally unresolvable wavelengthconflicts exist between “eastbound” express wavelengths and eastboundadd wavelengths, then operator proceeds to ROADM site #2. Else,conflicts on the eastbound fibre need to be manually resolved.

C) At ROADM site #2 and #3: Repeat same procedure as at ROADM site #1.

D) Repeat steps (A)-(C) starting at terminal site #2 and workingwestbound at ROADM sites 3, 2, then 1, sequentially performing theself-configuration procedure for the WSS devices employed to receive thewestbound traffic.

The invention has been described hereinabove with reference to specificembodiments as illustrated in the accompanying drawings. Although theauto-configuration method in its various embodiments has been describedhereinabove primarily (but not exclusively) as initiated by a discreteuser intervention, or by a software-imitated control signal at a systemstart-up. Alternatively, the method may be applied as a continuouscontrol algorithm, where presence of wavelengths is continuouslymonitored, and the WSS device configuration changed automatically as theinput conditions, i.e. wavelengths present, change.

It should be understood that each of the preceding embodiments of thepresent invention may utilize a portion of another embodiment, and manyother embodiments and variations of the method may be envisioned withinthe scope of the present invention. An ordinary person in the art wouldbe able to construct such embodiments without undue experimentation inlight of the present disclosure.

1. A method for operating a wavelength selective switch (WSS) device ina wavelength division multiplexed (WDM) optical network, the WSS devicehaving an output optical port and a plurality of input optical ports,and being coupled to a WSS controller for selectively provisioningoptical connections between the input optical ports and the outputoptical port at one or more of a plurality of supported wavelengths, themethod comprising: a) determining which of the supported wavelengths arereceived at each of the input ports using at least one optical channelmonitor (OCM) coupled to the WSS device; and, b) using the WSScontroller to selectively provision optical connections from respectiveinput optical ports to the output optical port at those of the supportedwavelengths that are received at a single input optical port of the WSSdevice, and to block connections between the input optical ports and theoutput optical port at those of the supported wavelengths that are notreceived at any of the input optical ports.
 2. The method of claim 1,wherein step b) comprises: c) receiving, by the WSS controller,information from the at least one OCM which of the supported wavelengthsare present at at least one of the input optical ports; d) based on theinformation received from the at least one OCM, determining by the WSScontroller which of the received wavelengths are present at one and onlyone of the input optical ports; and, e) at each of the wavelengthsidentified in step (d), provisioning by the WSS controller an opticalconnection in the WSS device between a corresponding input optical portand the output optical port.
 3. The method of claim 2, furthercomprising using the WSS controller to identify, based on theinformation received from the at least one OCM, a wavelength conflictwherein one of the supported wavelengths is detected at two or more ofthe input ports.
 4. The method of claim 3, further comprising at leasttemporarily blocking optical connections between each of the input portsand the output port at the one of the supported wavelengths for whichthe wavelength conflict is identified.
 5. The method of claim 4, furthercomprising: generating a wavelength conflict alarm when the presence ofthe one of the supported wavelengths at the two or more of the inputports is detected by the at least one OCM; and. Responsive to a userinput resolving the wavelength conflict, provisioning an opticalconnection, at the one of the supported wavelengths for which thewavelength conflict was identified, between the output port and one ofthe two or more input ports receiving said wavelength in accordance withthe user input.
 6. The method of claim 3 wherein the two or more of theinput ports are assigned different priorities, further comprising usingthe WSS controller to provision an optical connection in the WSS device,at the one of the supported wavelengths for which the wavelengthconflict was identified, between the output port and a selected one ofthe two or more input ports receiving said wavelength that is selectedaccording to the assigned priorities.
 7. A wavelength selective switch(WSS) device comprising: a WSS element having an input port and aplurality of output ports for selectively switching any of a pluralityof supported wavelength from any of the input ports to the output portor for blocking thereof, a WSS controller coupled to the WSS element forcontrolling the switching, and one or more optical channel monitors(OCM) coupled to the input and/or output ports of the WSS element and tothe WSS controller, wherein the WSS controller is programmed toauto-configure the WSS element when the WSS device is connected to anoptical WDM network, by performing the steps of: co-operating with theone or more OCM to detect the presence of the supported wavelengths ateach of the input ports; and, controlling the WSS element in such a waythat i) any the supported wavelengths that is not detected by the OCM atany of the input ports is blocked by the WSS element from reaching theoutput port; ii) any wavelength whose presence is detected by the OCM atone and only one of the input ports is switched to the output port; and,iii) any supported wavelength whose presence is detected at more thanone of the input ports is either blocked at each of the input portsuntil user intervention, or is blocked at all but one of the input portsand is directed to the output port from a single one of the input portsreceiving said wavelengths which has a comparatively higher priorityassigned thereto.